[time-nuts] Question about effect of spurious frequency modulation on Allan Deviation

Dana Whitlow k8yumdoober at gmail.com
Mon Aug 6 10:18:42 EDT 2018


One might also do some trials based on comparing ADEV results between a
clean carrier signal
and ones corrupted with varying degrees of FM (for example), to get a feel
for the problem.  If
nothing else, one ought to be able to get some feel for the sensitivities
involved.

Dana     K8YUM


On Mon, Aug 6, 2018 at 8:17 AM, jimlux <jimlux at earthlink.net> wrote:

> On 8/5/18 11:22 PM, Poul-Henning Kamp wrote:
>
>> --------
>> In message <84a802ff-88f1-5f50-1f79-71d8ba3c42c6 at rubidium.dyndns.org>,
>> Magnus D
>> anielson writes:
>>
>> What does exists is a formula for how a single sine spur would produce
>>> ADEV. A FM deviation with low enough modulation index creates two
>>> side-bands of opposite sign but same amplitude.
>>>
>>
>> I find the easiest way to wrap my head around this is to think
>> about measuring Adev by timing zero-crossings.
>>
> <snip>
>
>> Depending on the modulation signal, there may be moments where the
>> zero-crossing is "where it should be", for instance if the modulation
>> is sine or triangular, but not if it is a signed square wave.
>>
>>
>
>
> What about doing some sort of fit to the measurement data before
> calculating the ADEV? Similar to removing a linear ramp.
>
> basically you'd solve for the three sine parameters (f, phase,
> amp/deviation), then remove that from the data, then run the ADEV
> calculation.
>
>
>
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